The long range goal of this research program is to study mechanisms responsible for maintenance and restoration of the intestinal barrier. Intestinal ischemia/reperfusion injury is characterized by acute breakdown of the intestinal barrier. However, preliminary studies indicate that prostaglandins signal a remarkably rapid recovery of epithelial barrier function via the second messengers Ca2+ and cyclic AMP. Our central hypothesis is that prostaglandins I2 and E2 (PGI2 and PGE2) are elaborated by cyclooxygenase-2 (COX-2) during intestinal injury from sub-epithelial fibroblasts and restore barrier function by signaling closure of inter-epithelial tight junctions. Tight junctions close in response, to a synergistic signal between intracellular and cyclic AMP, which are increased by PGI2-stimulated cholinergic nerves and PGE2 receptor-linked adenylate cyclase respectively. The aims of this research are: to determine if PGI2 and PGE2 increase transepithelial resistance in ischemic-injured epithelium by a specific action on tight junctions; to determine the neural and epithelial receptor pathways by which PGI2 and PGE2 signal recovery of transepithelial resistance; and to determine the cellular and enzymatic source of prostaglandins responsible for rescuing epithelial barrier function. Two distinct injury models will be used: ischemic-injured intestinal mucosa and oxidant-damaged epithelial monolayers. Tissues will be mounted in Ussing chambers, and transepithelial electrical resistance will be monitored as an indicator of epithelial integrity. Radio-labeled fluxes will be used to determine the contribution of tight junction closure and restitution. Mechanisms by which prostaglandins signal repair will be tested by measuring second messengers and by blocking epithelial and neural signaling pathways. The cellular source of reparative prostaglandins will be determined by immunohistochemistry and fibroblast monolayer studies. Inhibition of COX-2 will be used to determine the contribution of distinct cyclooxygenases in the repair response. These experiments will provide insight into the signaling pathways and mechanisms by which prostaglandins trigger repair of acutely-injured intestinal epithelium.